GENOMIC DISTRIBUTION OF 5'-TTCCA 3'-REPEAT MOTIF AND ITS DIAGNOSTIC POTENTIAL IN HUMAN Y-CHROMOSOME-RELATED ANOMALIES

We have studied genomic distribution of a simple repeat motif 5' TTCCA 3' derived from the DYZ1 fraction of the human Y chromosome employing restriction fragment length polymorphism and in situ hybridization te chniques. This has led us to develop a synthetic DNA based genetic mar ker specific to human genome. Randomly selected human genomic DNA from both sexes, digested with a total of 16 restriction enzymes, hybridiz ed with OAT20Y probe comprising four repeat units of 5' TTCCA 3' motif failed to reveal fragment length polymorphisms. In contrast, with mos t of the enzymes, several multilocus monomorphic bands and with a few enzymes, smeary signals were detected. In situ hybridization of the OA T20Y probe with human chromosomes revealed grains on the long arm of t he Y chromosome, whereas the X-chromosome and autosomes showed random distribution of the grains without any preferential labeling in the ce ntromeric or telomeric regions. The OAT20Y probe uncovers a 3.4 kb iso morphic band exclusively in the human male DNA digested with Hae III e nzyme, Using the OAT20Y probe, we have detected the presence of Y chro mosome in mosaic cell populations of Turner's patients with dysgenetic gonads and high levels of LS/FSH. The presence of Y chromosome in the se patients has been associated with an increased risk of gonadoblasto ma. The OAT20Y probe offers sensitivity and accuracy for the detection of Y-chromosome-bearing cells in a mosaic cell population and, conseq uently, help in better management of the patients.